Track locking method for optical pickup head

ABSTRACT

A track locking method for use in an optical disc device comprising a pickup head. The pickup head comprises an actuator equipped with an optical lens controlling a laser focus on the optical disc. The pickup head is moved to a predetermined position. A track error signal in the optical disc device is detected. Whether a flicker frequency of the track error signal is less than a threshold is determined. Based on the determination, the actuator is provided with a braking force to pre-deviate the optical lens, and a track locking signal is delivered to the actuator and control parameters of the pickup head is stored to lock the laser focus on a destination track of the optical disc.

BACKGROUND

The invention relates to a track locking method for an optical pickup head, in particular, to a track locking method that pre-deviates an optical lens on the actuator before locking a track based on the flicker frequency of a track error signal detected by the optical pickup head.

Conventionally, the surface and axis of an optical disc may not be uniformly distributed, and may suffer from eccentricity producing periodic radial and axial oscillations. Radial oscillations induce track flicker, and axial oscillations affect focus of the laser of the optical pickup head. A track locking mechanism is thus desirable to accurately focus on the destination track.

FIG. 1 shows a conventional optical disc device. Optical disc 11 is driven by a spindle motor 12, and a pickup head (PUH) 16 comprising an actuator 26 is borne by a sled mechanism 14. The actuator 26 is equipped with an optical lens 20 that focuses the laser. The optical lens 20 is kept in the center of a case 18 such that physical impact can be avoided. A CPU 22 coordinates operation of the described components.

The optical disc 11 comprises a plurality of tracks 24, and through PUH 16, data located at the destination track 24 a is read. This operation, referred to as track seeking, is accomplished by a sled mechanism 14 moving the PUH 16 substantially above the destination track 24 a, that is, a predetermined position. Thereafter, track locking is executed by an actuator 26. The actuator 26 accurately and rapidly tunes the position of the optical lens 20 with incremental axial and radial adjustments. The actuator receives a track locking signal to control the radial movement, and a focus signal to control the axial movement.

FIG. 2 shows the position of the PUH 16. Before track locking, the PUH 16 is distributed around point c, vibrating between point a and b due to disc deviation (This phenomenon, so called “run-out effect”). d1 and d2 denote the distance therebetween, substantially identical. The relative speed between the PUH 16 and the optical disc 11 is minimal at point a and b, and is maximal at point c. Conventionally, track locking is not executed until the relative speed therebetween is less than a threshold calculated from a track error signal. The flicker frequency of the track error signal, such as 13 k per second, is proportional to the relative speed, such that the track locking can be based thereon. The actuator 26 is controlled by a track locking signal to lock the optical lens 20 at point a or b.

FIGS. 3 a and 3 b show the movement of the optical lens 20. Initially, the optical lens 20 is in the case center 32, locked on point a of the optical disc 11, generating vibration 30, in which the vibration center 36 deviates from the case center 32. When another track seek and lock take place, because the actuator 26 responds faster than the sled mechanism 14, the optical lens 20 may complete the next track locking before the sled mechanism 14 moves to the proper position. As a result, inward deviation from the case center 32 be increased, finally contacting the wall of case 18, inducing unexpected problems. Similarly, in another example, FIGS. 4 a and 4 b show the movement of the optical lens 20. The optical lens 20 may lock on the point b, with outward deviation also inducing the same problem. This phenomenon means that the PUH 16 is not always at case center 32 when track is locked, comprising two cases, inward deviation and outward deviation. When the optical disc device receives a sudden impact, which causes actuator 26 to lose a fix on destination track 24 a, and data reading process is interrupted, such that another track seek and lock are required.

SUMMARY

In view of the foregoing description, an embodiment of the invention provides a track locking method for use in an optical disc device comprising a pickup head, and optical disc device utilizing the method. The pickup head comprises an actuator equipped with an optical lens controlling laser focus on the optical disc, and the method comprises the following steps. The pickup head is first moved to a predetermined position, and determining a track error signal in the optical disc device. Providing a braking force to pre-deviate the optical lens when a flicker frequency of the track error signal exceeds a threshold, and keeping determining the flicker frequency. Delivering a track locking signal and storing control parameters of the pickup head to lock the laser focus on a destination track

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and not intended to limit the invention solely to the embodiments described herein, will best be understood in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of a conventional optical disc device;

FIG. 2 shows run-out effect of an optical disc;

FIG. 3 a and FIG. 3 b show inward deviation in a conventional optical disc device;

FIG. 4 a and FIG. 4 b show outward deviation in a conventional optical disc device;

FIG. 5 is a block diagram of an optical disc device according to an embodiment of the invention;

FIG. 6 is a flowchart of the track locking method; and

FIG. 7 shows the vibration of the optical lens according to an embodiment of the invention.

DETAILED DESCRIPTION

An embodiment of the invention provides a track locking method for use in an optical pickup head. The method pre-deviates an optical lens on an actuator before locking a track based on the flicker frequency of a track error signal detected by the optical pickup head. After track seeking in an optical disc device, if the relative speed of the optical pickup head and an optical disc is not within a range required by the track locking operation, a deviation force or braking force is applied to the optical lens of actuator for use as an initial state for the upcoming track locking operation. The concept is to pre-generate offsets, thus after track locking, the optical lens is positioned directly above the center of the optical pickup head. When another track seek and lock take place, the optical pickup head can accurately access a destination track.

FIG. 5 shows an optical disc device system according to an embodiment of the invention, with optical disc 11 is driven by spindle motor 12, sled mechanism 14 drives PUH 16 to move radially, wherein PUH 16 comprises an actuator 26 comprising optical lens 20, and the actuator 26 controls radial and axial movements of the optical lens 20 by magnetic coils. The PUH 16 also comprises a case 18 surrounding the optical lens 20 for protection. The CPU 22 coordinates the above components, and the memory 32 stores programs needed by CPU 22 for operation. In the embodiment, the track locking method for optical pickup head is implemented by programs stored in the memory 32. The actuator 26 is controlled by a track locking signal and a focus signal, focusing a laser on a destination track 24 a of an optical disc 11. Through signals transmitted by optical lens 20, CPU 22 identifies relative movements between the laser focus and the optical disc 11, and flicker frequency of the movement.

FIG. 6 is a flowchart of the track locking method according to an embodiment of the invention. In step 60, a destination track 24 a is selected through data allocation, and in step 62, the sled mechanism 14 moves the PUH 16 substantially above the destination track 24 a, that ism moves the PUH16 to a predetermined position. Steps 60 and 62 essentially constitute track seeking. Spindle motor 12 spins under control of CPU 22, operating with relative movement between the axis of optical disc 11 and PUH 16 caused by deviation generating flicker.

In step 64, a track error signal of the optical disc is detected; thereby track locking is executed according to the flicker frequency of the track error signal. If flicker frequency is low enough, for example, less than 13 kilohertz per second, the speed of relative movements between the optical disc and PUH 16 is low enough to proceed to step 70. Conversely, if the flicker frequency goes too high, more than 13 kilohertz per second, indicating the speed of relative movements between the optical disc and the PUH 16, track locking is unable to be performed, and the process goes to step 66. Flicker frequency meeting a threshold is the essential condition whether track locking can be performed, and the threshold is not limited to the embodiment here and can be designed according to practical system implementations, that is, the threshold is programmable.

In step 66, the actuator 26 pre-deviates optical lens 20 pre-deviated by applying a deviation force or a braking force thereon. The direction of deviation varies with the polarity of flicker frequency. As a problem the conventional method suffered, for example, when flicker frequency is positive due to the PUH 16 moving away from the axis 28 of the optical disc 11, track locking will cause optical lens 20 of actuator 26 to experience inward deviation. To solve the problem, in step 66, the optical lens 20 is pre-deviated outward by sending a track locking signal with a first value to the actuator 26, applying a braking force to pre-deviate the optical lens 20 outward. Conversely, when PUH 16 moves toward the axis 28 of the optical disc 11, track locking will cause the optical lens 20 of actuator 26 to experience an outward deviation, thus a track locking signal with a second value is sent to the actuator 26, applying a braking force to pre-deviate the optical lens 20 inward. Braking force can be designed according to practical system implementations or laboratory diagnosis.

In step 68, the flicker frequency is recursively determined. Unlike step 64, only when the flicker frequency is lower than the threshold, can the process go to step 70. During step 68, the braking force in step 66 is constantly applied to the optical lens 20.

In step 70, track locking is executed. Control parameters of the PUH 16 are stored, and appropriate track locking signals are delivered to keep the laser focus of PUH 16 tight with the destination track. A particular note is, step 68 and step 64 provide step 70 with different initial states, especially the track locking signal. When step 64 goes to step 70, the track locking signal is zero, and when step 68 goes to step 70, the value of track locking signal is the first value or the second value, such that corresponding braking force can be provided in step 66.

When the optical lens 20 deviates inward, after track seeking, if flicker frequency is determined to exceed the threshold, the track locking signal is set to a first value. As a result, a braking force is applied to optical lens 20 to pre-deviate outward. And the flicker frequency determination keeps running. When flicker frequency is lower than the threshold, track locking is executed with a braking force corresponding to the first value. Identically, when the optical lens 20 deviates outward, after track seeking, if flicker frequency exceeds the threshold, the track locking signal is set to a second value. As a result, a braking force is applied to optical lens 20 to pre-deviate inward. And the flicker frequency determination keeps running. When flicker frequency is lower than the threshold, the track locking is executed with the braking force corresponding to the second value.

FIG. 7 shows the track vibration of the optical lens according to the embodiment of the invention. The optical lens 20 accurately vibrates around the center 36 in the case 18. The deviation of the optical lens is eliminated. According to the described embodiments of the invention, inward and deviation effects are prevented by previously applying a braking force as an initial state of the track locking operation. Contrary to the prior art, no complicated logic control circuits are needed for implementation, which is economic and efficient.

While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A track locking method for use in an optical disc device comprising: moving a pickup head to a predetermined position; determining a track error signal in the optical disc device; providing a braking force to pre-deviate an optical lens when a flicker frequency of the track error signal exceeds a threshold, and keeping determining the flicker frequency; and delivering a track locking signal and storing control parameters of the pickup head to lock the laser focus on a destination track when the flicker frequency is less than the threshold.
 2. The track locking method as claimed in claim 1, wherein the threshold is 13 kilohertz per second.
 3. The track locking method as claimed in claim 1, further comprising, if the flicker frequency is less than the threshold when the pickup head reaches the predetermined position, setting the track locking signal to zero.
 4. The track locking method as claimed in claim 1, further comprising: if the flicker frequency exceeds the threshold and the optical lens deviates inward when reaches the predetermined position, setting the track locking signal to a first value, such that the optical lens is pre-deviated outward; and if the flicker frequency exceeds the threshold and the optical lens deviates outward when reaches the predetermined position, setting the track locking signal to a second value, such that the optical lens is pre-deviated inward; wherein the polarities of the first value and the second value are opposite.
 5. An optical disc device, comprising: a pickup head comprising an actuator, reading data from an optical disc, wherein the actuator is equipped with an optical lens controlling focus of a laser; a processor controlling the pickup head and the actuator; and a memory storing a program, whereby the processor executes to process the following steps: moving the pickup head to a predetermined position; determining a track error signal in the optical disc device; applying a braking force on the actuator to pre-deviate the optical lens when a flicker frequency of the track error signal exceeds a threshold, and keeping determining the flicker frequency; and delivering a track locking signal to the actuator and storing control parameters of the pickup head to lock the laser focus on a destination track when the flicker frequency is less than the threshold.
 6. The optical disc device as claimed in claim 5, wherein the threshold is 13 kilohertz per second.
 7. The optical disc device as claimed in claim 5, wherein: if the flicker frequency is less than the threshold when the pickup head reaches the predetermined position, the processor sets the track locking signal to zero.
 8. The optical disc device as claimed in claim 5, wherein: if the flicker frequency exceeds the threshold and the optical lens deviates inward when reaches the predetermined position, the processor sets the track locking signal to a first value, such that the optical lens is pre-deviated outward; and if the flicker frequency exceeds the threshold and the optical lens deviates outward when reaches the predetermined position, the processor sets the track locking signal to a second value, such that the optical lens is pre-deviated inward; when the flicker frequency is less than the threshold, the processor delivers the track locking signal to the actuator and stores control parameters of the pickup head; and the polarities of the first value and the second value are opposite.
 9. A track locking method for use in an optical pickup head, comprising: detecting a track error signal of the optical pickup head when the optical pickup head is at a predetermined position; applying a braking force to pre-deviate an optical lens when a flicker frequency of the track error signal exceeds a threshold, and keeping determining the flicker frequency; and delivering a track locking signal and storing control parameters of the pickup head to lock the laser focus on a destination track of the optical disc when the flicker frequency is less than the threshold.
 10. The track locking method as claimed in claim 9, wherein the threshold is 13 kilohertz per second.
 11. The track locking method as claimed in claim 9, further comprising, if the flicker frequency is less than the threshold when the pickup head reaches the predetermined position, setting the track locking signal to zero.
 12. The track locking method as claimed in claim 9, further comprising: if the flicker frequency exceeds the threshold and the optical lens deviates inward when reaches the predetermined position, setting the track locking signal to a first value, such that the optical lens is pre-deviated outward; and if the flicker frequency exceeds the threshold and the optical lens deviates inward when reaches the predetermined position, setting the track locking signal to a second value, such that the optical lens is pre-deviated inward; wherein the polarities of the first value and the second value are opposite. 